The present invention relates to a vertical shaft-type impact crusher and an operation method for a vertical shaft-type impact crusher. More particularly, the present invention relates to a vertical shaft-type impact crusher and an operation method for a vertical shaft-type impact crusher for crushing bulk materials, for example, natural rock, into grains or particles of desired size.
Bulk materials, e.g., natural rock, are crushed in accordance with various uses, for example, aggregate for concrete, paving stone, subgrade material, etc. One type of crusher used for such a crushing process is known as a vertical shaft-type impact crusher.
Impact crushers operate on the basis of the principle that rock is accelerated at a high speed so as to collide with an impact surface, thereby crushing the rock. Such impact crushers may be generally divided into two types according to the mode of crushing: anvil-type and dead stock-type.
The anvil-type impact crusher includes a rotor having a plurality of wings or blades on the upper side thereof which are rotated at a high speed, whereby raw stones east into the crusher are accelerated by the blades and centrifugally discharged so as to collide with anvils which are disposed annularly around the rotor, thereby crushing the raw stones.
Such an anvil-type impact crusher is mainly used for the purpose of crushing raw stones having a relatively large diameter by collision to thereby reduce the size of the raw stones.
On the other hand, a dead stock-type impact crusher is mainly used to smooth surfaces of raw stones which have already been crushed into gravel of desired size and to make the grain size uniform. Such a dead stock-type impact crusher is similar to the anvil-type impact crusher in that the raw stones are centrifugally accelerated by blades, but different from the latter in that dead stocks are formed from crushed raw stones at the periphery of the rotor, and the surfaces formed by this dead stock have angles of rest which are used as impact surfaces for crushing raw stones.
Aggregate for concrete is required to be made of crushed stone of a large grain size and crushed sand of small grain size. According to JIS (Japanese Industrial Standard), it is required for both stone and sand to be in given definite grain size distributions. The distribution of Crushed Stone JIS 5005 is defined as the weight-percentage of stones passing through sieves as follows:
______________________________________ 60 mm: 100%; 50 mm: 95 to 100%; 25 mm: 35 to 70%; 15 mm: 10 to 30%; and 5 mm: 0 to 5%. ______________________________________
It is difficult for an anvil-type impact crusher to produce stones of a large grain size and to produce stones having good shape, while it is difficult for a dead stock-type impact crusher to produce stones of a small grain size.
A further problem is that tips are worn by accelerated stones. A rotor is provided with pairs of tips mounted on the wings thereof. Stones of a large size, the diameter of which is larger than 40 mm, generate more chipping-type wear than stones of a small size. Material harder to chip is preferably applied for tips which are used in a crusher for crushing stones of a large size. Stones of small size, the diameter of which is smaller than 40 mm, generate more erosive-type wear than stones of a large size. A higher degree of erosive wear-resistant material is preferably applied for tips which are used in a crusher for crushing stones to a small size. As such, there is an inconsistency in the tips used in impact crushers for large sized stone-crushing and those used for small sized stone-crushing.